Crosslinked carboxyl group-containing polymers, alkyl-modified carboxyl group-containing polymers, and the like are known examples of carboxyl group-containing polymers to be used as thickening agents for cosmetics or the like, as humectants for cataplasms, and as suspension stabilizers for emulsions, suspensions or the like. Known examples of the crosslinked carboxyl group-containing polymers include copolymers of an α,β-unsaturated carboxylic acid, such as acrylic acid, and a polyallyl ether (cf. Patent Document 1), copolymers of an α,β-unsaturated carboxylic acid and hexaallyl trimethylene trisulfone (cf. Patent Document 2), copolymers of an α,β-unsaturated carboxylic acid and glycidyl methacrylate or the like (cf. Patent Document 3), copolymers of an α,β-unsaturated carboxylic acid and pentaerythritol allyl ether (cf. Patent Document 4, Patent Document 5, and Patent Document 6), and copolymers of an α,β-unsaturated carboxylic acid, a (meth)acrylic acid ester, and pentaerythritol allyl ether (cf. Patent Document 7 and Patent Document 8).
Known examples of the alkyl-modified carboxyl group-containing polymers include copolymers of a polyacrylic acid or (meth)acrylic acid and a (meth)acrylic acid alkyl ester, among others. More specifically, the known examples include copolymers obtained by reacting a specific amount of an olefinically unsaturated carboxylic acid monomer with a specific amount of a (meth)acrylic acid alkyl ester (the alkyl group containing 10 to 30 carbon atoms) (cf. Patent Document 9) and copolymers obtained by reacting an olefinically unsaturated carboxylic acid monomer with a (meth)acrylic acid alkyl ester (the alkyl group containing 8 to 30 carbon atoms) (cf. Patent Document 10).
In using the carboxyl group-containing polymer particle including crosslinked carboxyl group-containing polymers, alkyl-modified carboxyl group-containing polymers or the like in the aforementioned fields of application, it is first necessary to prepare a uniform aqueous dispersion of the carboxyl group-containing polymer particles and then neutralize the dispersion with an alkali to give a neutralized viscous liquid with a concentration of about 0.1 to 1% by mass. However, the aforementioned carboxyl group-containing polymer particles have a drawback that, as they are generally in the form of a fine powder, undissolved lumps are readily formed upon dispersing the particles in water. Once the undissolved lumps have been formed, a gel-like layer is formed on the surface of each lump and therefore the rate of permeation of water into the inside thereof is reduced. As a result, it becomes difficult to obtain a uniform aqueous dispersion.
For the aforementioned reasons, in preparing an aqueous dispersion of carboxyl group-containing polymer particles, it is necessary to include an unproductive procedure of gradually adding powders of the carboxyl group-containing polymer particles to water under high-speed stirring for preventing the formation of undissolved lumps. Moreover, in some cases, a special dissolution apparatus may be required for preventing the formation of undissolved lumps.
Furthermore, as the carboxyl group-containing polymer particles mentioned earlier are in the form of a fine powder and are readily charged electrically, the polymer particles cause heavy dusting. Therefore, the carboxyl group-containing polymer particles mentioned earlier have disadvantages that they are not only difficult to handle but are not suitable for the working environment as well. Furthermore, the carboxyl group-containing polymer particles in fine powder form problematically have low bulk density and therefore cause an increase in transportation cost and require an increased number of storage sites.
For the reasons mentioned earlier, the advent of a granular carboxyl group-containing polymer particle has been awaited.
In granulating a powder, a granulator is generally used. The granulators are broadly classified into three types, that is, mixing granulation, forced granulation and granulation utilizing heat depending on methods of granulation to choose.
Examples of the granulators for mixing granulation include a fluidized bed granulator and a tumbling granulator. Those granulators produce granules by allowing powders to float and flow by means of an air stream or stirring blade or by tumbling while uniformly spraying the powders with a liquid serving as a binder. When an attempt is made to apply these granulators for mixing granulation to the carboxyl group-containing polymer particles, since the carboxyl group-containing polymer particles are very small in particle size and low in bulk density, it is difficult to allow those particles to float and flow by means of an air stream or stirring blade or by tumbling. The liquid serving as a binder is preferably water or a polar organic solvent. However, when the floating and flowing carboxyl group-containing polymer particles are sprayed with water or the polar organic solvent, the carboxyl group-containing polymer particles get sticky and adhere to inside walls of the granulator or a binder-spraying nozzle, or stick to one another to form large undissolved lumps.
Examples of the granulators for forced granulation include a compression molding granulator and an extrusion granulator. As the method for granulating the carboxyl group-containing polymer particles utilizing forced granulation, a method including compressing fine powders using a compression molding machine, followed by grinding (cf. Patent Document 11) may be exemplified. However, this method has a problem that, for example, the carboxyl group-containing polymer particles are excessively compressed by the pressure exerted by the compression molding machine, and as a result, the swelling property of the resulting granular carboxyl group-containing polymer particles in water is deteriorated.
Examples of the granulator for granulation utilizing heat include a spray dryer. A spray dryer, however, has problems, for example, that it is economically disadvantaged due to the need for dilution of the carboxyl group-containing polymer particles with water, an organic solvent or the like to a viscosity level at which the diluted product can be sprayed, and that the granule to be obtained is not porous and thus poor in solubility in water.
On the other hand, examples of known methods for granulation without using the granulators mentioned earlier are the method including bringing fine powders of a polymer flocculant into contact with water vapor for granulation (cf. Patent Document 12), the method including dispersing fine powders of a water-soluble polymer in an organic solvent and then adding water for granulation (cf. Patent Document 13), and the method including feeding a lubricant and water simultaneously and continuously to a water-soluble polymeric substance in fine powder form and grinding the thus-granulated gel bodies (cf. Patent Document 14). In the case of the carboxyl group-containing polymer particles, however, it is difficult to apply those methods because of problems such as the problem (1): the carboxyl group-containing polymer particles, when brought into contact with water formed due to dew condensation of water vapor, swell with the water, and thus the finally-obtained granule is not porous and has poor solubility in water, and additionally the problem that, in the method including allowing powders to fall to contact with water vapor, it is difficult to allow the carboxyl group-containing polymer particles to uniformly fall due to the poor flowability thereof and a large amount of dust may possibly be flung up upon allowing the powder to fall; the problem (2): on the occasion of adding water following dispersing the particles in an organic solvent, the resulting hydrous gel forms undissolved lumps; and the problem (3): since the granule contains an unnecessary lubricant depending on use and is produced via a gel form, the granule obtained is not porous and has poor solubility in water.
Patent Document 1: U.S. Pat. No. 2,923,629
Patent Document 2: U.S. Pat. No. 2,958,679
Patent Document 3: Japanese Kokai Publication Sho-58-84819 (JP-A 58-84819)
Patent Document 4: U.S. Pat. No. 5,342,911
Patent Document 5: U.S. Pat. No. 5,663,253
Patent Document 6: U.S. Pat. No. 4,996,274
Patent Document 7: Japanese Kokoku Publication Hei-05-39966 (JP-B 05-39966)
Patent Document 8: Japanese Kokoku Publication Sho-60-12361 (JP-B 60-12361)
Patent Document 9: Japanese Kokai Publication Sho-51-6190 (JP-A 51-6190)
Patent Document 10: U.S. Pat. No. 5,004,598
Patent Document 11: WO 03/016382
Patent Document 12: Japanese Kokai Publication Sho-52-2877 (JP-A 52-2877)
Patent Document 13: Japanese Kokai Publication Sho-52-136262 (JP-A 52-136262)
Patent Document 14: Japanese Kokai Publication Hei-03-143605 (JP-A 03-143605)